(1) Field of the Invention
The present invention relates to a Sixe2x80x94SiC material of Si concentration-gradient type and a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, both superior in properties such as weatherability, oxidation resistance, creeping resistance, strength, toughness and the like, as well as to processes for production of said materials.
(2) Description of Related Art
In the midst of rapid progress of technological innovation, big projects are being planned and carried out in various parts of the world for development of state-of-the-art technologies such as space shuttle and space plane (in the field of space development), high-temperature combustion gas turbine (in the field of energy) and high-temperature gas furnace and nuclear fusion reactor (in the field of atomic energy).
Also, utilization of hydrogen energy is being studied in order to use it as an energy other than nuclear energy and solar energy. In this connection, expensive metal or fine ceramic is being investigated to use it as a reactor material. These structural materials must have high strength at intermediate to high temperatures (200 to 2,000xc2x0 C.), high reliabilities in toughness and impact resistance, and resistances to environment (e.g. corrosion resistance, oxidation resistance and radiation resistance).
Currently, as a ceramic superior in heat resistance, there are newly developed ceramics, i.e. silicon nitride and silicon carbide both having high strength. They, however, are inherently fragile and are very fragile even when there have small flaws, and further have low resistance to thermal or mechanical impact.
In order to overcome these drawbacks of the above ceramics, there was developed a ceramic matrix material (CMC) wherein a continuous ceramic fiber is mixed with a ceramic. This material, having high strength and high toughness even at high temperatures, excellent impact resistance and excellent resistances to environment, is under active study as a structural material having an ultrahigh resistance to heat, in Europe, U.S.A., etc.
For example, there was developed a ceramic matrix composite (CMC) wherein a fiber was mixed into a ceramic matrix, by making ceramic long fibers (ordinarily several hundreds to several thousands fibers) having a diameter of about 10 xcexcm, into a fiber bundle (a yarn), arranging these fiber bundles two-dimensionally or three-dimensionally to form a unidirectional sheet or a cloth, or laminating a plurality of such sheets or such cloths to form a preliminary molded material (a fiber preform) having a desired shape, and forming, inside the preliminary molded material, a matrix by, for example, (a) chemical vapor infiltration or (b) inorganic polymer infiltration and sintering, or filling the inside of the preliminary molded material with a ceramic powder by casting and sintering the resulting material to form a matrix inside the preliminary molded material.
In the sintering (firing) used in production of conventional ceramic matrix material, however, no attention was paid to the CO gas generated in the process, and it was conducted only to introduce an inert gas by a slight pressure control mainly for prevention of Si vaporization.
Consequently, the CO gas produced during firing in association with the conversion of organic polymer into ceramic, by the reaction of free carbon (present in firing atmosphere) and O2 and the reaction of free carbon and SiO2, is liberated to form defects; these defects and the growth of xcex2-SiC crystals bring about significant deterioration of strength; further, the pores in produced ceramic matrix material cannot be reduced to zero and their size is as large as about 1 mm, inviting deterioration of weatherability and oxidation resistance.
Further, although the conventional ceramic matrix material contains a SiC fiber inside, the thermal stress which the material receives during actual use, is caused by the difference in thermal expansion between SiC fiber and Sixe2x80x94SiC moiety; therefore, the material has had laminar peeling in some cases.
In view of the above-mentioned problems of the prior art, the present invention has been completed with objects of providing:
a Sixe2x80x94SiC material of Si concentration-gradient type and a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, both significantly improved in corrosion resistance in highly oxidative and corrosive environment, strength, and healability of defects of surface layer and innermost layer, and
processes for production of the above materials.
The further objects of the present invention are to provide:
a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, which has substantially no pore unlike ceramic matrix materials (CMC) having pores, such as SiC fiber-reinforced Sixe2x80x94SiC composite material obtained by CVD or infiltration of inorganic polymer and which is improved in toughness while having the features of Sixe2x80x94SiC sintered materials, such as high oxidation resistance, creeping resistance, and strength and toughness from ordinary temperature to high temperatures, and
a process for production of the above material.
According to the present invention, there is provided a Sixe2x80x94SiC material of Si concentration-gradient type obtained by melt-infiltrating Si into a molded material comprising SiC particles, which Sixe2x80x94SiC material has a porosity of 1.0% or less and in which Sixe2x80x94SiC material the Si concentration decreases gradually from the surface layer towards the innermost layer.
In the above Sixe2x80x94SiC material of Si concentration-gradient type, it is preferred that the ratio of the Si concentration of the surface layer and the Si concentration of the innermost layer is in a range of innermost layer/surface layer=0/100 to 90/100.
According to the present invention, there is also provided a process for producing a Sixe2x80x94SiC material of Si concentration-gradient type by melt-infiltrating Si into a molded material comprising SiC particles, which process comprises preparing at least two kinds of mixtures each comprising SiC particles having a different tap density, laminating the mixtures to form a molded material, keeping the molded material and Si at a temperature of 1,100 to 1,400xc2x0 C. in an inert gas atmosphere, and then increasing the temperature to 1,500 to 2,500xc2x0 C. to melt-infiltrate Si into the molded material.
In the above process, it is preferred that the molded material and Si are kept at a temperature of 1,100 to 1,400xc2x0 C. at a pressure of 0.1 to 10 hPa for at least one hour with an inert gas being flown in an amount of 0.1 NL or more per kg of the total of the molded material and Si and then the temperature is increased to 1,500 to 2,500xc2x0 C. to melt-infiltrate Si into the molded material. The inert gas is preferably Ar.
According to the present invention, there is also provided a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type obtained by melt-infiltrating Si into a molded material comprising a SiC fiber and SiC particles, which composite material has a porosity of 1.0% or less and in which composite material the Si concentration decreases gradually from the surface layer towards the innermost layer.
In the above SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, it is preferred that the ratio of the Si concentration of the surface layer and the Si concentration of the innermost layer is in a range of innermost layer/surface layer =0/100 to 90/100.
Also in the above SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, the oxygen content of the SiC fiber is preferably 0.5 mass % or less and the SiC fiber may have a form of two-dimensional or three-dimensional cloth.
According to the present invention, there is also provided a process for producing a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type obtained by melt-infiltrating Si into a molded material comprising a SiC fiber and SiC particles, which process comprises preparing at least two kinds of mixtures each comprising SiC particles having a different tap density, mixing a SiC fiber into each mixture, laminating the resulting mixtures to form a molded material, keeping the molded material and Si at a temperature of 1,100 to 1,400xc2x0 C. in an inert gas atmosphere, and then increasing the temperature to 1,500 to 2,500xc2x0 C. to melt-infiltrate Si into the molded material.
In the above process for producing a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, it is preferred that the molded material and Si are kept at a temperature of 1,100 to 1,400xc2x0 C. at a pressure of 0.1 to 10 hPa for at least one hour with an inert gas being flown in an amount of 0.1 NL or more per kg of the total of the molded material and Si and then the temperature is increased to 1,500 to 2,500xc2x0 C. to melt-infiltrate Si into the molded material. The inert gas is preferably Ar.
In the Sixe2x80x94SiC material of Si concentration-gradient type and the SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type both of the present invention, the porosity is almost zero (1.0% or less) and the Si concentration decreases gradually from the surface layer towards the innermost layer.
Thereby, the present materials have excellent corrosion resistance in highly oxidative or corrosive environment and excellent strength, and are significantly improved in healability of defects of surface layer and innermost layer.
Description is first made on the process for production of the present Sixe2x80x94SiC material of Si concentration-gradient type.
The Sixe2x80x94SiC material of Si concentration-gradient type of the present invention is obtained by melt-infiltrating Si into a molded material comprising SiC particles.
The properties of the Sixe2x80x94SiC material of Si concentration-gradient type differ depending upon the structure of the molded material into which Si is to be melt-infiltrated. Therefore, the production method of the molded material is very important and it is preferred to produce the molded material according to the following method.
Compaction molding as one example of the production method of the molded material used in the present process is described below.
The main raw material of the molded material is SiC granulated particles obtained by subjecting, to granulation by spray drying or the like, a mixture comprising SiC coarse particles having an average particle diameter of 50 to 100 xcexcm, SiC fine particles having an average particle diameter of 0.1 to 10 xcexcm and, desirably, a carbon powder having an average particle diameter of 0.1 to 30 xcexcm. Preferably, at least two kinds of SiC granulated particles different in tap density are appropriately selected and used.
Incidentally, xe2x80x9ctap densityxe2x80x9d is a bulk specific gravity obtained when a powder is placed in a container and shaken or tapped for a given length of time for stabilization.
SiC granulated particles having a tap density of 0.7 to 0.85 are filled in a given mold and subjected to press molding or the like to prepare preliminary molded material 1.
In the same manner are prepared preliminary molded material 2 comprising SiC granulated particles having a tap density of 0.85 to 1.00 and preliminary molded material 3 comprising SiC granulated particles having a tap density of 1.00 to 1.3.
As shown above, the tap densities of the SiC particles of the preliminary molded materials 1 to 3 are set so as to be xe2x80x9cpreliminary molded material 1 less than preliminary molded material 2 less than preliminary molded material 3xe2x80x9d.
Then, these preliminary molded materials are made into a molded material. In that case, it is important that the preliminary molded material comprising SiC particles of the smallest tap density forms the surface layer of the molded material and that the innermost layer of the molded material is formed by at least one preliminary molded material comprising SiC particles having a tap density larger than that of the surface layer. Also, it is preferred that the preliminary molded materials are disposed so that the tap density of SiC particles increases gradually from the surface layer of the molded material towards the innermost layer.
For example, the preliminary molded materials are disposed so as to form a sandwich structure of xe2x80x9cpreliminary molded material 1-preliminary molded material 2-preliminary molded material 1xe2x80x9d or xe2x80x9cpreliminary molded material 1-preliminary molded material 3-preliminary molded material 1xe2x80x9d or xe2x80x9cpreliminary molded material 1-preliminary molded material 2-preliminary molded material 3-preliminary molded material 2-preliminary molded material 1xe2x80x9d; then, press molding is conducted to produce a laminated molded material.
Further, cast molding as other example of the production method of the molded material used in the present process is described below.
First, as main materials of the molded material, there are prepared slurries by adding an organic binder and water to a mixture comprising SiC coarse particles having an average particle diameter of 50 to 100 xcexcm, SiC fine particles having an average particle diameter of 0.1 to 10 xcexcm and, desirably, a carbon powder having an average particle diameter of 0.1 to 30 xcexcm. Preferably, few to several kinds of slurries different in the proportion (weight %) of the SiC coarse particles and the SiC fine particles (these two kinds of SiC particles are main materials of each slurry) are appropriately selected and used.
Specifically, there are prepared slurry A comprising the SiC coarse particles (20 to 40% by weight) and the SiC fine particles (80 to 60% by weight), slurry B comprising the SiC coarse particles (40 to 60% by weight) and the SiC fine particles (60 to 40% by weight), and slurry C comprising the SiC coarse particles (60 to 80% by weight) and the SiC fine particles (40 to 20% by weight).
The total amount of SiC particles (the SiC coarse particles and the SiC fine particles) in each of slurries A to C is constant. Therefore, when the proportion (weight %) of the SiC coarse particles is high, the proportion (weight %) of the SiC fine particles is low; and when the proportion (weight %) of the SiC coarse particles is low, the proportion (weight %) of the SiC fine particles is high.
Next, a molded material is produced using these slurries. In that case, it is necessary that a slurry comprising the SiC coarse particles in the highest proportion (weight %) is disposed so as to form the surface layer of the molded material and that the innermost layer of the molded material is formed so as to comprise the SiC coarse particles in a proportion (weight %) smaller than that in the surface layer and the SiC fine particles in a proportion (weight %) larger than that in the surface layer. Preferably, the innermost layer of the molded material is formed so that in a position closer to the center of the molded material, the proportion (weight %) of the SiC coarse particles is smaller and the proportion (weight %) of the SiC fine particles is larger.
In an example, slurries A to C are cast into a given mold so as to form a sandwich structure of xe2x80x9cslurry A-slurry B-slurry Axe2x80x9d or xe2x80x9cslurry A-slurry C-slurry Axe2x80x9d or xe2x80x9cslurry A-slurry B-slurry C-slurry B-slurry Axe2x80x9d, whereby a laminated molded material is produced.
In melt-infiltrating Si into the molded material produced by any of the above two processes, since the molded material is produced so that the innermost layer has a smaller porosity (Si is later infiltrated into these pores) than the surface layer has, the concentration of Si infiltrated can be made smaller from the surface layer towards the innermost layer, that is, the Si concentration can have a gradient. The ratio of the Si concentration of the innermost layer and the Si concentration of the surface layer can be allowed to be in a range of innermost layer/surface layer 0/100 to 90/100.
The laminated molded material produced as above is kept, together with Si, in a firing furnace at a temperature range of 1,100 to 1,400xc2x0 C. at a pressure of 0.1 to 10 hPa for at least one hour with an inert gas being flown in an amount of 0.1 NL (normal liter) (corresponding to 5,065 liters of 1,200xc2x0 C. and 0.1 hPa), whereby a molded material to be impregnated with Si is produced.
Next, the molded material to be impregnated with Si is heated to a temperature of 1,500 to 2,500xc2x0 C., preferably 1,700 to 1,800xc2x0 C. to melt-infiltrate Si thereinto, to produce a Sixe2x80x94SiC material of Si concentration gradient-type according to the present invention.
In the present process for production of Sixe2x80x94SiC molded material of Si concentration-gradient type, it is desirable that the molded material and Si are kept in a firing furnace at a temperature of 1,100 to 1,400xc2x0 C. at a pressure of 0.1 to 10 hPa for at least one hour with an inert gas being flown in an amount of 0.1 NL or more, preferably 1 NL or more, more preferably 10 NL or more per kg of the total of the molded material and Si.
Thus, by conducting the firing stage (a stage prior to Si melting and infiltration) in an inert gas current, the gas (e.g. CO) generated in conversion of inorganic polymer or inorganic substance into ceramic is removed from the firing atmosphere and, moreover, the pollution of the firing atmosphere with external factor (e.g. O2 in air) is prevented; as a result, the Sixe2x80x94SiC material of Si concentration-gradient type obtained by subsequent melt-infiltration of Si into molded material can have substantially zero porosity.
In melt-infiltration of Si into the fired molded material, the atmosphere temperature is increased to 1,500 to 2,500xc2x0 C., preferably 1,700 to 1,800xc2x0 C. In this case, the pressure inside the firing furnace is preferably 0.1 to 10 hPa.
As stated above, in the Sixe2x80x94SiC material of Si concentration-gradient type, since the Si concentration is high in the innermost layer as compared with that in the surface layer, the microcracks appearing in the material can be healed. As a result, the material can retain oxidation resistance.
Further, in the Sixe2x80x94SiC material of Si concentration-gradient type, the surface layer is made of a protective film completely impregnated with Si. Therefore, the material has remarkably improved corrosion resistance in a highly oxidative and corrosive environment and the surface defects can be made smaller and removed. As a result, the material has even improved strength in a highly oxidative and corrosive environment.
Description is then made on the process for production of the present SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type.
The SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type of the present invention is obtained by melt-infiltrating Si into a molded material comprising a SiC fiber and SiC particles.
The properties of the SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type differ depending upon the structure of the molded material into which Si is to be melt-infiltrated. Therefore, the production method of the molded material is very important and it is preferred to produce the molded material according to the following method.
Compaction molding as one example of the production method of the molded material used in the present process is described below.
First, fine SiC fibers (ordinarily several hundreds to several thousands fibers) having a diameter of about 10 xcexcm are made into a fiber bundle (a yarn); and these fiber bundles are arranged two-dimensionally or three-dimensionally to form a unidirectional sheet or a cloth, or such sheets or such cloths are laminated to form a fiber preform having a desired shape.
The main raw material of the molded material is SiC granulated particles obtained by subjecting, to granulation by spray drying or the like, a mixture comprising SiC coarse particles having an average particle diameter of 50 to 100 xcexcm, SiC fine particles having an average particle diameter of 0.1 to 10 xcexcm and, desirably, a carbon powder having an average particle diameter of 0.1 to 30 xcexcm. Preferably, at least two kinds of SiC granulated particles different in tap density are appropriately selected and used.
SiC granulated particles having a tap density of 0.7 to 0.85 are arranged in a layer with the above-obtained fiber preform being placed in the middle of the layer so as to form a sandwich structure, and subjected to press molding or the like to prepare preliminary molded material 1.
In the same manner are prepared preliminary molded material 2 comprising SiC granulated particles having a tap density of 0.85 to 1.00 and preliminary molded material 3 comprising SiC granulated particles having a tap density of 1.00 to 1.3.
As shown above, the tap densities of the SiC particles of the preliminary molded materials 1 to 3 are set so as to be xe2x80x9cpreliminary molded material 1 less than preliminary molded material 2 less than preliminary molded material 3xe2x80x9d.
Then, these preliminary molded materials are made into a molded material. In that case, it is important that the preliminary molded material comprising SiC particles of the smallest tap density forms the surface layer of the molded material and that the innermost layer of the molded material is formed by at least one preliminary molded material comprising SiC particles having a tap density larger than that of the surface layer. Also, it is preferred that the preliminary molded materials are disposed so that the tap density of SiC particles increases gradually from the surface layer of the molded material towards the innermost layer.
For example, the preliminary molded materials are disposed so as to form a sandwich structure of xe2x80x9cpreliminary molded material 1-preliminary molded material 2-preliminary molded material 1xe2x80x9d or xe2x80x9cpreliminary molded material 1-preliminary molded material 3-preliminary molded material 1xe2x80x9d or xe2x80x9cpreliminary molded material 1-preliminary molded material 2-preliminary molded material 3-preliminary molded material 2-preliminary molded material 1xe2x80x9d; then, press molding is conducted to produce a molded material.
Further, cast molding as other example of the production method of the molded material is described below.
First, fine SiC fibers (ordinarily several hundreds to several thousands fibers) having a diameter of about 10 xcexcm are made into a fiber bundle (a yarn); and these fiber bundles are arranged two-dimensionally or three-dimensionally to form a unidirectional sheet or a cloth, or such sheets or such cloths are laminated to form a fiber preform having a desired shape.
Then, as main materials of the molded material, there are prepared slurries by adding an organic binder and water to a mixture comprising SiC coarse particles having an average particle diameter of 50 to 100 xcexcm, SiC fine particles having an average particle diameter of 0.1 to 10 xcexcm and, desirably, a carbon powder having an average particle diameter of 0.1 to 30 xcexcm. Preferably, few to several kinds of slurries different in the proportion (weight %) of the SiC coarse particles and the SiC fine particles (these two kinds of SiC particles are main materials of each slurry) are appropriately selected and used.
Slurry A comprising the SiC coarse particles (20 to 40% by weight) and the SiC fine particles (80 to 60% by weight) is cast into a given mold in which the above-obtained fiber preform has been placed, to impregnate the fiber preform with the slurry, whereby preliminary molded material A is produced.
In the same manner, there are produced preliminary molded material B by using slurry B comprising the SiC coarse particles (60 to 40% by weight) and the SiC fine particles (40 to 60% by weight), and preliminary molded material C by using slurry C comprising the SiC coarse particles (60 to 80% by weight) and the SiC fine particles (40 to 20% by weight).
In the slurries A to C of the preliminary molded materials A to C, the total amount of SiC particles (the SiC coarse particles and the SiC fine particles) is constant. Therefore, when the proportion (weight %) of the SiC coarse particles is high, the proportion (weight %) of the SiC fine particles is low; and when the proportion (weight %) of the SiC coarse particles is low, the proportion (weight %) of the SiC fine particles is high.
Next, a molded material is produced using these preliminary molded materials. In that case, it is necessary that a preliminary molded material comprising the SiC coarse particles in the highest proportion (weight %) is disposed so as to form the surface layer of the molded material and that the innermost layer of the molded material is formed with a preliminary molded material comprising the SiC coarse particles in a proportion (weight %) smaller than that in the surface layer and the SiC fine particles in a proportion (weight %) larger than that in the surface layer. Preferably, the innermost layer of the molded material is formed so that in a position closer to the center of the molded material, the proportion (weight %) of the SiC coarse particles is smaller and the proportion (weight %) of the SiC fine particles is larger.
For example, the preliminary molded materials are 19 disposed so as to form a sandwich structure of xe2x80x9cpreliminary molded material A-preliminary molded material B-preliminary molded material Axe2x80x9d or xe2x80x9cpreliminary molded material A-preliminary molded material C-preliminary molded material Axe2x80x9d or xe2x80x9cpreliminary molded material A-preliminary molded material B-preliminary molded material C-preliminary molded material B-preliminary molded material Axe2x80x9d; then, press molding is conducted to produce a molded material.
In melt-infiltrating Si into the molded material produced by any of the above two processes, since the molded material is produced so that the innermost layer has a smaller porosity (Si is later infiltrated into the pores) than the surface layer has, the concentration of Si infiltrated can be made smaller from the surface layer towards the innermost layer, that is, the Si concentration can have a gradient. The ratio of the Si concentration of the innermost layer and the Si concentration of the surface layer can be allowed to be in a range of innermost layer/surface layer=0/100 to 90/100.
The molded material produced as above is kept, together with Si, in a firing furnace at a temperature range of 1,100 to 1,400xc2x0 C. at a pressure of 0.1 to 10 hPa for at least one hour with an inert gas being flown in an amount of 0.1 NL (normal liter) (corresponding to 5,065 liters of 1,200xc2x0 C. and 0.1 hPa), whereby a molded material to be impregnated with Si is produced.
Next, the molded material to be impregnated with Si is heated to a temperature of 1,500 to 2,500xc2x0 C., preferably 1,700 to 1,800xc2x0 C. to melt-infiltrate Si thereinto, to produce a SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration gradient-type according to the present invention wherein a SiC fiber and a Sixe2x80x94SiC sintered material have been made into a composite material.
In the present process for production of SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type, it is desirable that the molded material and Si are kept in a firing furnace at a temperature of 1,100 to 1,400xc2x0 C. at a pressure of 0.1 to 10 hPa for at least one hour with an inert gas being flown in an amount of 0.1 NL or more, preferably 1 NL or more, more preferably 10 NL or more per kg of the total of the molded material and Si.
Thus, by conducting the firing stage (a stage prior to Si melting and infiltration) in an inert gas current, the gas (e.g. CO) generated in conversion of inorganic polymer or inorganic substance into ceramic is removed from the firing atmosphere and, moreover, the pollution of the firing atmosphere with external factor (e.g. O2 in air) is prevented; as a result, the SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type obtained by subsequent melt-infiltration of Si into molded material can have substantially zero porosity.
In melt-infiltration of Si into the fired molded material, the atmosphere temperature is increased to 1,500 to 2,500xc2x0 C., preferably 1,700 to 1,800xc2x0 C. In this case, the pressure inside the firing furnace is preferably 0.1 to 10 hPa.
As described above, the SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type according to the present invention is substantially free from pores which are present in conventional ceramic matrix materials (CMC) (e.g. SiC fiber-reinforced Sixe2x80x94SiC composite materials) produced by CVD or inorganic fiber infiltration; therefore, the present composite material, as compared with conventional ceramic matrix materials (CMC), is dense and moreover retains excellent features of Sixe2x80x94SiC sintered material, such as oxidation resistance, creeping resistance, strength from ordinary temperature to high temperatures and toughness. Further, in obtaining a bonded ceramic material from a plurality of non-oxide ceramic members (e.g. Si-based ceramics) containing an excessive amount of an element participating in bonding, by allowing a metal to be present between said members to be bonded and heating them in a non-oxidizing atmosphere to form a compound of (1) said element participating in bonding and (2) said metal at the portion where said bonding is to be made, according to a procedure as described in Japanese Patent Application Kokai (Laid-Open) No. 128046/1994, the SiC fiber-reinforced Sixe2x80x94SiC composite material of Si concentration-gradient type of the present invention, since having a Si-rich layer at the surface, can enable ceramic-to-ceramic bonding easily.
Furthermore, the present composite material can be used in an article such as crucible for chemical liquid, or the like. In that case, the surface of the present composite material is used as the inside of the crucible which comes in contact with the liquid, and the innermost layer of the present composite material is used as the outside of the crucible which makes no contact with the liquid.